Conventional golf balls can be divided into two general classes: solid and wound. Solid golf balls include one-piece, two-piece (i.e., single layer core and single layer cover), and multi-layer (i.e., solid core of one or more layers and/or a cover of one or more layers) golf balls. Wound golf balls typically include a solid, hollow, or fluid-filled center, surrounded by a tensioned elastomeric material, and a cover.
Examples of golf ball materials range from rubber materials, such as balata, styrene butadiene, polybutadiene, or polyisoprene, to thermoplastic or thermoset resins such as ionomers, polyolefins, polyamides, polyesters, polyurethanes, polyureas and/or polyurethane/polyurea hybrids, and blends thereof. Typically, outer layers are formed about the spherical outer surface of an innermost golf ball layer via compression molding, casting, or injection molding.
From the perspective of a golf ball manufacturer, it is desirable to have materials exhibiting a wide range of properties, such as resilience, durability, spin, and “feel,” because this enables the manufacturer to make and sell golf balls suited to differing levels of ability and/or preferences. In this regard, playing characteristics of golf balls, such as spin, feel, CoR and compression can be tailored by varying the properties of the golf ball materials and/or adding additional golf ball layers such as at least one intermediate layer disposed between the cover and the core. Intermediate layers can be of solid construction, and have also been formed of a tensioned elastomeric winding. The difference in play characteristics resulting from these different types of constructions can be quite significant.
Golf balls are generally made by forming outer layers about an interior layer via one or more of injection molding, casting and compression molding. Compression molding typically involves cross-sectioning a length of extrudate into a plurality of preforms/slugs, molding the preforms/slugs into half-shells, and then mating a pair of half-shells about each preform/slug under sufficient heat and pressure.
Heretofore, lengths of extrudate have been cross-sectioned at predetermined intervals by a rotating straight-edge flying knife-type blade while the extrudate progresses on an assembly line in a direction that is perpendicular to the direction that the straight-edge flying knife-type blade is rotating. Examples of such a conventional straight-edged flying knife-type blade include blade 3 of FIG. 1B, discussed herein below, and/or blade 22 of U.S. Pat. No. 5,596,251 of Miller (“'251 patent”)(for cutting molten plastic material), hereby incorporated herein in its entirety.
The resulting conventional preforms have cross-sectioned faces that are flat/level to very slightly curved due to forces which act on the extrudate as it progresses along the assembly during cross-sectioning. This flat/level to very slightly curved surface contour changes substantially while being molded into a cup-shaped half-shell.
Unfortunately, such preforms can fill out in the mold unsatisfactorily while making this big shape adjustment and produce a half-shells having irregularities such as a non-uniform thickness. And when those half-shells are then compression molded about a subassembly, the subassembly can be off-center, which negatively impacts golf ball flight and putting characteristics as well as creates golf ball durability problems.
Accordingly, there is a need for improved preform face shapes that more closely match, follow or resemble the ultimate cup-shaped contour of a half-shell which would reduce the amount of change a preform has to undergo while being molded into a half-shell. Such preforms, and methods of making, if meanwhile producible and implementable within existing compression molding and golf ball manufacturing processes, would be particularly desirable and useful. The accompanying inventive golf balls, preforms, half-shells, tooling and methods of making same address and solve this need.